Process of purifying phosphoric acid



Eux-E Nov. 8, 192 7.

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IIIIIIII Patented i Non.. gy i927'.

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"Application nuay novmbers, 1926. semi No. 146,312.v

The present invention relates to improve` 4ments in processes andapparatus for puriying phosphoric acid. I

The present application constitutes an nnprovernent of the applicationof George'A. Hendrie, v 2, A1,926. As in the Hendrie application abovereferred to, the process contemplates the purification of comparativelyimpure phosphoric acid produced'by treating, phosphoric rock withsulphuric acid which process is generally known as thewet-4 or Dorrprocess. The `rave/.phosphoric acid as produced by the Dorr processcontains a numthe Wet process.

ber of impurities including iron and aluminum compounds. y

The present invention is directed to an improved method for cheapeningthe puriication 'process heretofore used for reiining the raw phosphoricacid used as afresult of The 'drawings show a diagrammaticillustrationof the process andapparatus.

Referring to the dratvings,} designates a supply of phosphate4rock'vvhich isone of the raw materials used. Sulphuric acid can beproduced in any Well knovvnl manneras pure phosphoric acid is thencollected at 14:

hy the apparatus generally designated at 1 1. 'llhe sulphuric acid andphosphate rock are then treated in the Dorr mixer generally.des`:ignated at 12 from Which sludge is removed,` ro'rntime to time asindicated at 13. lm-

and passes to a minerai; 15; Carbonaceous A material in the form of coalor coke is sup-v plied from a supply 16 to a pulvcrizer 17.. (Crudephosphate roch is also suppliediroin 10 as indicated lutto thepulverizer 17 and this phosphate roch is there ground up with thecoal or'colse and admitted to the mine-i115. lin this mixer the phosphate rochre-acts and 'combinesyvith the crude phosphcric acid to formmono-calcium phosphate and from thev miner 115 the .monoscalciumphosphate thus produced together with the coal creche is passed? to aheater or dryer 20. vlin this heater, moisture is driven orf asindicated at 21 and the mono-calcium phosphate is converted tc a calciummetaphosphate. l rom .dryer the calcium metaphosphate and the pulverizedcoal or Serial No. 133,111, filed September this retort furnace thecalcium-metaphosphate re-acts With the carbon as follows:

P41 plus 1,0 0,0

. Sca (P0312, plus 10C equals ACaal (POQ plus heating value can beutilized for heating the dryer 2O and the furnace/ 22. From time totime, the phosphorus is apped oil from the phosphorus condenser 2 andlead into the phosphorus `storage reservoir 24:. 1t is desired that aconsiderablel'storage capacity be provided for the phosphorus as thesucceeding apparatus consumes the phosphorus at a rapid rate and it isdesired .that s ucient storage be provided toipermit considerablecollection to be obtainediA lf desired, a num= ber of phosphorusproducing units can be used as with a single phosphorus storage tank andwith a single phosphorus coverting unit. rllhe phosphorus fromthestorage reservoir 24 isadmitted into 'a converter 25 receiving steamat. 26 andlconverting the phosphorus into commercially pure phosphoricacid which is discharged into a collecting chamber 27. Q The hydrogenevolved may be' collected 'in a suitable hydrogen gas holder lt will beunderstood tha taking place in the converter 25 is that de-v scribed inthe Liljenroth Patenty #1,59d72, dated August 3, 1926. As previouslystated, the retort furnace 22 converts the calcium metaphosphate intotri-calcium phosphate. lin this conversion the various unfdesirableimpuritiesinclud-ing the objectionable iron andaluminum compounds remainwith thetri-calcuin phosphate and when the t the reaction re-actioniscomplete this :tric'alcium lphos- .phate roxnthe -:furnace 22 isreturned in part to the-phosphate roch` supply pile 10l and in partdirectto the pulverizer 17. lln practice f from 10 to20vper cent of thetri-calcium phosphat@ 'with' theimpurities can rbe returned to the pile10, and 80 to 90 rcent can be admitted to-thepulvcrizer 1 Thetri-calcium phosphate can thus.be again used in the process. As theprocess is continued, the impurities which are removed from the rawphosphoric acid will gradually increase in this tri-calcium phosphateformed by the retort furnace 22 and we therefore, contemplate theremoval of this impure tri-calcium phosphate' at times. Such removal canbe eected either continually, a certain percentage being.

removed for each operation cycle, or preferably an entire charge oftri-calcium phosphate can be removed and disposed of and not readmittedto the initial steps' ofthe process. A

In practice it will be Afound that after lthe .process is continued fora certain time with the tri-calcium phosphate returned and reused, thatthis tri-calcium phosphate will contain a considerable percentage ofiron phos phide and such iron phosphi'de can be separated out from thetri-calcium phosphate in any desired manner and separately disposed Bythe above process the crude phosphoric correspondingly.

What we claim is: y

1. The process of purifying crude lphosphoric aci'dwhich comprisesmixing impure acid with carbonaceous material and phosphate rock,e'ecting a conversion of the tricalcium phosphate into mono-calciumphosphate and then into calcium metaphosphate, heating the mixture toform phosphorus and leave with the tri-'calcium hosphate the impuritiesinitially present in t e phosphoric acid, converting the phosphorus intocom-v' ymercially pure phosphoric acid, and returning and recovering thetri-calcium-phosphate -in'the initial steps of the process and 1nremoving the accumulated impurities by a removal of the tri-calciumphosphate afterthe heating step.-

2. The processor purifying crude phosphoric acid'l which comprisesmixing the imp ure acid with carbonaceousf material and phosphate rock,converting theV tri-calcium phosphate into mono-calcium phosphate,subsequently converting the mono-calcium phosphate into calciummetaphosphate, heating the. mixture to effect a. conversion of themono-calcium phosphate into tri-calcium phosphate with the evolution ofphosphorus,

converting the phosphorus into commercially pure "phosphorouspentoxideand withdrawing the impurities rwith the tri-calcium phosphate which isproduced said heating step.

by thel afore- 3.4v The process of purifying crude phosphoric acid whichcomprises mixing impure acid with carbonaceous material and phosphaterock, eecting the conversion of the tri-calcium hosphate into mono andthe calcium metap sphate, and subsequently heating the mixture to formtrilcalcium'phosphate and to evolve phosphorus which is available forconversion into commercially pure phos hor- I ous -pentoxide, returningthe -.trica cium phosphate to the initial steps of the-process and `inwithdrawing tri-calcium phosphate after the heating-step when they carrythe collected impurities which were initially present with the crudephosphoric acid.

In testimony signatures.

ERNEST E. PEVEEE. GEORGE A. HENDRIE.

whereof we hereto aiiix our

